Recent Advances in Trace Elements

Comprehensive and multidisciplinary presentation of the current trends in trace elements for human, animals, plants, and the environment

This reference provides the latest research into the presence, characterization, and applications of trace elements and their role in humans, animals, and plants as well as their use in developing novel, functional feeds, foods, and fertilizers. It takes an interdisciplinary approach to the subject, describing the biological and industrial applications of trace elements. It covers various topics, such as the occurrence, role, and monitoring of trace elements and their characterization, as well as applications from the preliminary research to laboratory trials.

Recent Advances in Trace Elements focuses on the introduction and prospects of trace elements; tackles environmental aspects such as sources of emission, methods of monitoring, and treatment/remediation processes; goes over the biological role of trace elements in plants, animals, and human organisms; and discusses the relevance of biomedical applications and commercialization.

• A compendium of recent knowledge in interdisciplinary trace element research
• Uniquely covers production and characterization of trace elements, as well as the industrial and biomedical aspects of their use
• Paves the way for the development of innovative products in diverse fields, including pharmaceuticals, food, environment, and materials science
• Edited by well-known experts in the field of trace elements with contributions from international specialists from a wide range of areas

Unique in presenting comprehensive and multidisciplinary information of the key aspects of trace elements research in a digestible form, this book is essential reading for the novice and expert in the fields of environmental science, analytical chemistry, biochemistry, materials science, pharmaceutical science, nutraceutical, and pharmaceutical sciences. It is also valuable for companies that implement new products incorporating trace elements to the market.

• Language: English
• Publisher: Wiley
• Release date: Feb 23, 2018
• ISBN: 9781119133803

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1

Introduction

Katarzyna Chojnacka

Wrocław University of Science and Technology, Faculty of Chemistry, Department of Advanced Material Technologies, Wrocław, Poland

1.1 Introduction

Trace elements (TEs), although present in low quantities, can have significant effects in living organisms. Although the role of trace elements in the human body is not yet fully understood, it is known that their effect on human health can be essential, neutral, or detrimental [1]. Trace elements play a role in many chemical, biochemical, and enzymatic reactions; biological and physiological, catabolic and metabolic processes of living organisms [2]. Their role relies on the unique property of them forming complexes and binding with macromolecules (e.g., proteins) [1]. Frequently mentioned trace elements or micronutrients are: Cr, Co, Cu, F, I, Mn, Mo, Se, V, and Zn. The main sources of these elements for humans are drinking water, food and food supplements, and the general environment. There are trace elements that are essential, but there are also those that are non‐essential or potentially toxic: Al, As, Cd, Hg, and Pb [2].

Humans are exposed to trace elements from atmospheric suspended particles in street and house dust to soil and are exposed through different routes such as inhalation, ingestion, or dermal adsorption. The establishment of emission standards for trace elements is important when considering the potential impact on society from urban areas, taking into account toxicity and the degree of human exposure [3].

1.2 Definition of Trace Elements (TEs)

Trace elements were first described at the beginning of the twentieth century as elements present at very low levels in different matrices. In actual fact, different branches of science (e.g., geochemistry, medicine, agriculture, and chemistry) have different understandings of TEs. The word trace is usually related to abundance, and includes elements with different chemical properties: elements and metalloids, including the micronutrients group, essential elements, and toxic elements. In geochemistry, TEs are chemical elements that occur in the earth’s crust in amounts less than 0.1% and to biological sciences TEs are elements present in trace concentrations in living organisms [4]. The result of these differences is that, until now, no precise definition of TEs has been provided. Elements that are trace in biological materials are not necessarily trace in terrestrial environments (e.g., iron) [4]. Early research theorized that these elements do not play important functions due to their low abundance [1] but, more recently, it has been shown that this is not the case.

1.3 Sources of Trace Elements for Humans

There are beneficial effects of TEs in food. However, in some cases, impurities in the food chain and in the general environment has been observed to have detrimental effects [1]. The relation between bioavailability and speciation in food is an important factor here, especially concerning iron, selenium, or chromium [1].

Vincevica‐Gaile et al. [2] reviewed the trace metal content in foods from plant (vegetables: carrots, onions, potatoes) and animal origin (cottage cheese, eggs, honey). Environmental factors (e.g., geographical location or seasonality), botanical origin, agricultural practices, product processing, and storage were all found to influence the content of TEs. The level of TEs in food depends on the environmental conditions of specific sites such as the composition of soil and water [2].

Tea plants contain high levels of TEs because they are grown in acidic soils where metal ions are more available for uptake by the root system. Some of the TEs (Al, Cu, Cd, Cr, Mn, and Ni) are beneficial; others are harmful for human health and are transferred through tea infusion. The content of tea has been assessed and found to show nutritional value, but also adverse health effects [5]. Tea contains 4–9% of inorganic matter, 30% of which is extracted. Polyphenolic compounds (flavonoids) bind metal ions, especially Fe and Cu [5]. The reported TE contents in fresh tea leaves are as follows (mg/kg): for example, Chinese tea [6]: Al 2034–3322, Cd 0.03–0.08, Cu 9.68–18.82, As 0.024–0.066, and Pb 0.31–3.42 [7] and Turkish tea: Mn 2617–3154 and Ni 6.60–11.7 [5, 8].

A good dietary source of TEs (Fe, Cu, Zn, and Mn) comes from seaweed. For instance, Porphyra vietnamensis can be added to foods to improve the content of essential minerals and trace elements. The strong flavor of seaweeds is related to the presence of TEs, the content of which is higher than in terrestrial vegetables. An example content of TEs in seaweed is: Fe 1260 mg/kg and Cu 7.46 mg/kg. The consumption of 8 g of green, brown, or red seaweed contains more than 25% of a daily Dietary Recommended Intake [9].

1.4 Analytical methods

Pollution of the environment with trace metals has generated the need for finding suitable analytical methods that are sensitive, rapid, effective, and reliable. Several analytical techniques; inductively coupled plasma‐atomic emission spectrometry (ICP–AES), inductively coupled plasma‐mass spectrometry (ICP–MS), atomic absorption spectrometry (AAS), x‐ray fluorescence (XRF), total reflection x‐ray fluorescence (TXRF) spectroscopy, and neutron activation analysis (NAA) have been developed to analyze and monitor trace elements in environmental and food samples, as well as in the human body [10]. The determination methods ICP‐OES, NAA, and ICP‐MS are techniques with high sensitivity and multi‐element capability [11]. TXRF is a quantitative analysis technique for liquid samples which can be deposited as thin films on clean reflectors. The sensitivity and detection limits of TXRF are better than XRF [10].

The unique chemical properties and coherent behavior of TEs means that their environmental distribution reflects geographical location and aquatic factors (e.g., source input and water–rock interaction). Similarities between trace metals and their very low concentrations do, however, make determination difficult. Problems appear if a particular element is evaluated in a mixture with other elements as interferences and coincidences can occur [11]. The matrix and elements that are to be analyzed dictate the how difficult an analysis may be. For example, the direct determination of REEs (Rare Earth Elements) in high‐salt groundwater, because the concentrations of REEs are close to the detection limit of ICP‐MS and there are high concentrations of matrix ions (K, Na, Ca, and Mg) which defocus the extracted ion beam due to space charge effects, means that significant losses of analyte sensitivity are produced [11].

For this reason, pre‐concentration techniques are used and separation from the matrix elements is required before ICP‐MS analysis takes place. Solid phase extraction (SPE) or solvent extraction (SE) techniques are employed for the pre‐treatment of high‐salt samples (e.g., seawater). This removes the matrix components and enriches the samples with analytes. Of course, this can generate a new matrix and new interferences [11].

Speciation of TEs is important in the analysis of food, quality of products, health, and environment. Mobility, bioavailability, storage, retention, and toxicity of TEs depends on their chemical form. Biochemical and geochemical pathways depend on speciation [1]. Of particular importance is characterizing speciation of TEs in samples related to the chemistry of life. This requires the elaboration of separation techniques, sensitive enough to determine elements, as well as the identification of metallo‐compounds [12]. The problem with speciation analysis is related to the low total concentration of TEs, for example, ng/L in serum. The level of given species can even be several times lower. Another problem lies within non‐covalent bonds that are formed by TEs in different matrices such as tissue, blood, urine, sediment, water, and sludge, that are unstable especially after sampling [1].

1.5 Toxicity

The toxicity of TEs depends not only on their concentration (dose), but also on their speciation. Safe and adequate daily intake (SAI), and acceptable daily intake (ADI) have been defined as important toxicological measures. Table 1.1 summarizes the important toxicological issues related to TEs together with guidelines for drinking water and daily intake.

Table 1.1 Trace elements and their toxicity [5, 13].

1.6 Trace Elements in Agriculture

Trace metals from soil can accumulate in less soluble forms and enter the food chain migrating from the soil and plant biota to humans and can move to watersheds through leaching and erosion [14]. Trace elements are taken up by plants and re‐enter the food chain or leach through the soil profile to groundwater. Organic matter in soil may increase the mobility of TEs [15]. Continuous harvesting of crops from fields interrupts the cycling of organic matter and depletes nutrients in the soil [15]. The level of TEs can be partially replenished by adding mineral fertilizers or composts. The addition of TEs to soil is regulated by guidelines recommending maximum levels in fertilizers and soils.

1.6.1 Trace Elements in Soil

Soils are sinks for TEs because many species of trace ions are fixed, a characteristic which determines how they are cycled in the soil [4]. The behavior of TEs in soil is fundamentally defined by their association with different soil components and phases [4]. Uptake by plants depends on the rate and amount of TEs applied as fertilizer, as well as soil and plant characteristics [16]. There are permanent physical, chemical, and biological processes occurring in soils that cause the evolution of parent materials, determine sorption, speciation, redistribution, mobility, and bioavailability of TEs. Weathering relies on the dissolving of primary minerals and hydrolysis of released elements [17].

A biohazard risk in soils is associated with the presence of trace metals, but not necessarily their total content. It is more relevant to determine fractions that describe their mobility and therefore whether real dangers to the abiotic and biotic elements of the environment are posed. Rao et al. [18] presented a review of the extraction schemes for trace metal fractionation in environmental samples (soil, sewage sludge, road dust and run off, waste, and miscellaneous materials) and recommended the use of chemometric methods in sequential extraction analysis [18].

1.6.2 Trace Elements in Fertilizers

Trace elements in fertilizers are categorized as either non‐essential in plant metabolism (Cd, Cr, Hg, Ni, Pb) or essential in trace quantities (Cu, Fe, and Zn). If TEs are found together with organic matter, they become organically‐bound and are less available to plants than mobile mineral forms [19]. Also, soil adsorptive properties determine bioavailability to plants. Many reports describe the impact of TEs on crop plants [19].

The aim of increasing agricultural productivity is the primary reason for using agricultural fertilizers containing TEs that might be toxic, can contaminate soils, and reach food products [20]. Concerns over food security are related to agricultural supplements and subsequent soil contamination which causes chemicals to accumulate in grocery products [20]. Quality control of fertilizers used in agricultural production is essential, since they can become contaminated by raw material, especially if they are recycled or are waste materials. The maximum permitted limits for contaminants (As, Cd, Cr, Hg, and Pb) in mineral fertilizers are regulated by law [20]. The general risk model for establishing safe levels of TEs in fertilizers includes evaluating: the content in fertilizer product, application rate, level in soil, uptake by plants, food ingestion rate for crops, established acceptable level in diet (toxicity), and the calculation of an acceptable upper limit of a specific TE in fertilizer products [16].

Many TEs are also fertilizer micronutrients. In the past, they have been introduced to soil mainly in the form of mineral salts. More recently, innovative, controlled released products have been designed. The idea is to supplement micronutrients in highly bioavailable and nontoxic form with minimum losses to the environment (leaching to groundwater). Biologically important TEs (Cu, Co, Mo) can be leached slowly from granulated phosphogypsum. Leachability depends on the presence of urea or urea phosphate [22].

Liu et al. [21] produced fertilizers with TEs chelated by amino acids, based on proteins of bacteria from sewage sludge. The method relied on hydrolysis by mineral acids and further chelation with TEs (Fe, Cu, Zn, Mn, Mom and B) [21].

Nziguheba and Smolders [14] analyzed 200 samples of phosphate fertilizers in order to estimate the input of trace metals to soils. The average concentrations (mg/kg) determined in fertilizers were: 14.8 (Ni), 7.4 (Cd), 166 (Zn), 2.9 (Pb), 7.6 (As), and 89.5 (Cr) [14]. A linear and positive correlation between the level of P and trace metal content was found. It was concluded that trace metal application using fertilizers was comparable to atmospheric deposition from the air [14].

Long‐term phosphate fertilizers contribute to the level of TEs in soil, in particular As, Cd, and Pb, and consequently the level seen in cultivated crops [16]. The levels of As, Cd, and Pb in phosphate fertilizers falls within the following ranges (respectively): 8–15, 3–12, 3–30 mg/kg [16]. Additional factors contributing to the level of TEs in soil include atmospheric deposition, incorporation of crop residues, and harvesting. However, there is a substantial difficulty in evaluating TEs inputs and outputs [16].

1.7 Environmental Aspects

1.7.1 Fuels

Trace elements are present in various types of fuel. During the combustion process they are transferred to either the ash or are emitted with flue gases.

Trace metals in petroleum products occur either in organic or inorganic form. Their presence is either of natural origin or may be added during refinery processing. The concentration of TEs can be determined by ICP‐OES and ICP‐MS techniques. Important issues in analysis include sample preparation, speciation, and total content analysis. The ratios between the levels of given metals are a sort of fingerprint that reflects the age of the oil and its origin (the V/Ni ratio in particular). The content of metals determines environmental risk and defines the use of a refining procedure (demetallization). The presence of metals can cause problems for engines, in particular for electronic sensors involved in the control of the combustion process. Some compounds of trace metals are added as antioxidants, anti‐icing agents, anti‐knock agents, or metal deactivators. Trace metals are added as additives or catalysts (Co, Cr, Mn, Mo, Ni, Sn, V, Zn), whereas others form contaminants during the refining process (Cr, Cu, Fe, Mn, Ni, Zn) or are of natural origin (Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Sn, V, Zn) [23].

Coal is a source of TEs. The composition of mineral matter in coal determines the environmental hazards associated with the emission of toxic TEs during coal combustion and utilization. The composition of coal is determined by how it formed. For example, peat which has accumulated and been influenced by seawater has a different composition than peat accumulated in a freshwater environment. The subsequent composition of elements is therefore connected to the peat‐swamp environment. Reports have been carried out on geochemical data using mineralogical studies (SEM, XRD) identifying the origin of TEs in coals [24].

1.7.2 Emissions from Waste

It is important to determine the content, mobility, and chemical association of TEs, as well as the chemical characteristics of various waste fuel incineration ashes, as these are important in predicting the migration behavior of TEs [25]. The release of TEs from waste incineration is a problem that limits its use or disposal. Another problem related to the presence of TEs in waste is their release which is affected by various geochemical characteristics: mineral composition, acid neutralization ability, weathering conditions, and the intrinsic properties of the elements themselves. Leachability is affected by leachate pH, liquid—solid ratio (L/S), extractant type and concentration, contact time, and solid matrix [25].

Charlesworth et al. [3] report on the sources, transport pathways, and sinks of particulate TEs in urban environments, paying particular attention to the atmosphere, soil, street and indoor dusts. The new discipline of urban biochemistry focuses on these aspects. The research shows that emissions of Pb, As, Cd, Hg, Zn, and Cu have significantly decreased in urban environments over the last few decades.

Saqib and Bäckström [25] investigated bottom ashes from different waste fuels and wood for the total content of TEs. This included looking at leaching behavior using a standard leaching procedure (EN 12457‐3) and the chemical association of TEs using sequential extraction. It was found that the type of fuel determined the level of TEs. The content, in decreasing order, was as follows: Cu > Zn > Pb > Cr > Ni > Sb > As [25].

1.7.3 Trace Elements in Sewage Sludge

Sewage sludge is being used as an alternative fuel in mono‐ or co‐combustion with coal. The retention and emission of TEs during combustion was investigated [28]. Fly ash was found to consist of very fine particles which provided sufficient specific surface area for TEs such as Pb, Cu, Zn, Cr, As, and Cd [26]. The research found that TEs can leach out from fly ash and cause soil and groundwater contamination, posing a great risk to human health and the environment. It is crucial therefore to control the mobility of TEs [26].

The content of the following TEs has been studied in sewage sludge: As, Cd, Co, Cr, Cu, Ni, Pb, Zn. The TEs are involved in chemical reactions and phase transition and therefore become enriched in the ash. In this process, Pb and Zn may undergo volatilization. For example, during co‐combustion of sewage sludge with coal gangue, crystalline kaolinite is broken into semi‐crystalline metakaolinite and then to mullite. The decomposition and transition of the crystal structure causes a charge imbalance and the elements become chemically bonded to the aluminosilicate structure. A result of this is that co‐combustion can facilitate the prevention of TEs emission [27].

The migration of TEs from fly ash from waste incineration is a problem for use and in landfill. The average total content of TEs in most fly ashes decreases in the order Zn > Cu > Pb > Sb > Cr > As > Cd. The most mobile elements that present excessive leaching are Cd, Pb, Zn, Cu, and Sb, as determined by sequential extraction [25].

1.8 Biomonitoring of Trace Metals in Surface Water

In environmental water biomonitoring studies, the following are considered as TEs: As, Ba, Cd, Cr, Cu, Ni, Pb, V, and Zn. The origin of these elements in coastal areas could be due to industrial activity: chemical and petrochemical plants, oil refineries, or harbor activities. Trace elements present in water reach marine ecosystems and pose ecological risks. The behavior of TEs in marine water is complex as these TEs can occur in different phases: colloidal, particulate, or dissolved phases. The latter is found in the lowest levels [27]. Monitoring programs have been established to track changes in the levels of trace metals in water environments. The presence of these metals affects fish and wildlife [28]. Biomonitoring techniques enable assessment of the biologically available levels of pollutants in ecosystems and, simultaneously, their effect on living organisms and their response to different environmental conditions over long periods of time.

Upwelling and the formation of geochemical provinces influence the presence, or not, of biogenic and other elements in surface waters. These are seen in the mineral composition of organisms living in these waters. The content of TEs (Fe, Mn, Zn, Cu, Cd, Pb, Ni, Cr) in brown algae, bivalves, and gastropods, as well as other organisms that inhabit water environments and foul navigation buoys has been studied and shown that the existence of biogeochemical provinces in the sea can be identified through the observation of higher concentrations of TEs in organisms [29].

Trace metals not only undergo bioaccumulation and biomagnification, but also biotransformation. Macrobenthic biomonitors fulfill the criteria for good biomonitors of TEs because of their limited mobility [27]. For instance, in aquatic environments Hg(II) is microbiologically converted to methylmercury, resulting in elevated concentrations in fish. Mercury concentration in the edible muscle of fish in many cases exceeds health guidelines for human consumption and may also be toxic to the fish itself [28].

Various organisms have developed protective mechanisms. For example, hepatocytes (cells in the liver) contain high levels of intracellular binding proteins and peptides which help to bind non‐essential metals, thus preventing their interaction with metabolic processes. It is possible to isolate subcellular fractions and investigate trace metal content there in order to investigate intracellular distribution. If non‐essential metals are found in potentially sensitive subcellular compartments, this could signify potential toxicological effects [28, 30].

1.9 Conclusions

Trace elements, although present in trace quantities can have a substantial effect not only on living organisms but also on processes occurring in the environment. Although we already have significant scientific knowledge concerning TEs, more research is undoubtedly needed in the science of accumulation, specification of uptake, and the effect of TEs on human health. Identifying the role of TEs and the mechanisms of their action is crucial in informing obligatory standards for regulating the level of TEs in the environment, in emissions, food, water, and industrial products. This is possible only through a combination of toxicological and environmental sciences and following an analysis of the current state of TEs in the environment, identification of the origin of TEs, and methods of preventing environmental contamination.

References

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2

Historical Aspects

Henryk Górecki and Katarzyna Chojnacka

Wrocław University of Science and Technology, Faculty of Chemistry, Department of Advanced Material Technologies, Wrocław, Poland

2.1 Introduction

It is difficult to give an unambiguous definition of trace elements (TEs). Different fields of science, or even areas of life, categorize elements in different ways. Different sets of elements are classified as trace in geology, biology, medicine, or agriculture.

According to definitions given in popular encyclopedias and dictionaries (e.g., Merriam‐Webster Dictionary) a trace element is a chemical element present in minute quantities. [1]. As a rule, the group of TEs includes a set of elements that have a small share in the total specified system. A spectacular example is the consideration of the composition of the earth's crust which consists of 89 elements, of which 99% of the mass contains 10 elements. The remaining 79 elements are shared in the remaining 1%.

2.2 Definitions of Trace Elements According to the Branch of Science

In life sciences TEs are defined as a chemical elements present in minute quantities used by organisms and are essential to their physiology (Collins English Dictionary) [2]. Taking into account their presence in the environment and their role in vital chemical processes, essential chemical elements can be grouped as basic elements: carbon (C), oxygen (O), nitrogen (N), phosphorus (P), sulfur (S), hydrogen (H); macronutrients: calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), chlorine (Cl); and trace elements: zinc (Zn), copper (Cu), iron (Fe), boron (B), manganese (Mn), molybdenum (Mo), titanium (Ti), chlorine (Cl). In addition to these elements essential to life, we also have to deal with elements of unwanted properties and negative effects on life. This applies primarily to the TEs such as lead (Pb), mercury (Hg), arsenic (As), cadmium (Cd), and beryllium (Be).

The content of TEs in ecosystems or in specific biological and environmental materials is much lower than that of the macronutrients.

Whether or not an element is considered a TE depends on the specific scientific discipline that studies the properties and the role of these elements. For example, in analytical chemistry the group of TEs includes elements whose concentration is less than 100 ppm (100 mg/kg). In geochemistry, geology, and petrography, the group of TEs includes the elements present in rocks and minerals at concentrations below 0.1% (1000 ppm). In minerals of sedimentary origin, as well as some elements, magma, including silicon, aluminum, iron are present in concentrations that correspond to basic elements, while in biological and environmental materials they are present as trace elements.

In life sciences, division of the group of TEs differs slightly from the agricultural sciences. In the field of life sciences, we can distinguish biogenic elements oxygen (O), hydrogen (H), carbon (C), nitrogen (N), phosphorus (P), sulfur (S), macronutrients calcium (Ca), potassium (K), sodium (Na), magnesium (Mg), chlorine (Cl), and the trace elements: iron (Fe), fluoride (F), zinc (Zn), silicon (Si), iodine (I), copper (Cu), manganese (Mn), chromium (Cr), selenium (Se), boron (B), molybdenum (Mo), nickel (Ni), vanadium (V), zinc (Zn), arsenic (As), cobalt (Co), strontium (Sr).

To qualify as a member of the group of TEs in biotechnology and medicine, TEs are considered as a dietary elements that are needed in very low concentrations for proper growth and development of organisms. In medicine, thanks to precise analytical methods with very low limits of detection in diagnosis and medical research, the contents of 72 elements from the group of TEs have been analyzed. In medicine, the research list of trace elements even extends to environmental factors, as well as those absorbed by the human respiratory system in the form of suspended particulates and gases (beryllium (Be), thallium (Tl), radon (Rn), vanadium (V)) and TEs present in drinking water, and also supplied via drugs or dietary supplements. Trace elements may be passed into the body via vaccines and implants (chromium (Cr), titanium (Ti)).

Chemical elements and their compounds are necessary for plant growth and plant metabolism. The basic plant macronutrients for photosynthesis are carbon and oxygen, which are absorbed from the air, and hydrogen, derived from water. Other nutrients are taken from the soil complex. Plants must obtain the mineral primary macronutrients from their growing base (soil): nitrogen (N), phosphorus (P), potassium (K); macronutrients (secondary and tertiary): calcium (Ca), sulfur (S), magnesium (Mg); and the micronutrients (TEs): iron (Fe) boron (B), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), sodium (Na), silicon (Si), selenium (Se), vanadium (V) aluminum (Al), nickel (Ni), titanium (Ti), chlorine (Cl). Macronutrients are present in plant tissue in concentrations between 0.2% and 4.0% (on a dry matter weight basis). Micronutrients are present in plant tissue in parts per million, ranging from 0.1 to 200 ppm, or less than 0.02% dry weight. In the soil environment, as well as in products used to fertilize and improve the soil structure, agrochemicals for plant protection are also compounds of elements that aren't necessary for plants. The presence of these elements in crops used as feed or directly as food is harmful to livestock and humans. Existing regulations limit the presence of elements such as arsenic (As), lead (Pb), cadmium (Cd), and mercury (Hg), both in the final agricultural products, as well as in the soil, in both plant protection products and fertilizers (Regulation (EC) No 2003/2003 of the European Parliament and of the Council of 13 October 2003 relating to fertilizers) [3]. A set of micronutrients presented is formed of 19 TEs, 4 of which are recognized as indispensable for the growth of plants, and 4 as undesirable. In animal nutrition and in food products a micronutrient collection should be supplemented with iodine.

In biochemistry, an ultratrace element is considered a chemical element that normally comprises less than one mg/g in biological samples including boron, silicon, nickel, vanadium and cobalt. The possible ultratrace elements in other organisms include bromine, cadmium, fluorine, lead, lithium, and tin. (Collins English Dictionary) [2].

Recent results of medical investigation indicate that boron (B), silicon (Si), nickel (Ni), vanadium (V), and cobalt (Co) can be added to the group of possible ultratrace elements found in the human body. Other possible ultratrace elements in other organisms include bromine (Br), cadmium (Cd), fluorine (Fl), lead (Pb), lithium (Li), and tin (Sn).

In the biological sciences the classification of elements is slightly different from the agricultural sciences. In this field, we can distinguish biogenic elements: oxygen (O), hydrogen (H), carbon (C), nitrogen (N), phosphorus (P), sulfur (S); macronutrients: calcium (Ca), potassium (K), sodium (Na), magnesium (Mg), chlorine (Cl); and the trace elements iron (Fe), fluoride (Fl), zinc (Zn), silicon (Si), iodine (I), copper (Cu), manganese (Mn), chromium (Cr), selenium (Se), boron (B), molybdenum (Mo), nickel (Ni), vanadium (V), zinc (Zn), arsenic (As), cobalt (Co), strontium (Sr), scandium (Sc), yttrium (Y), and elements occurring in the earth's surface, ground waters and drinking water in which the content of micronutrients is limited by water quality regulations. Natural waters include the following trace elements: arsenic (As), beryllium (Be), boron (B), cadmium (Cd), chromium (Cr), copper (Cu), fluoride (Fl), iodine (I), iron (Fe), lead (Pb), manganese (Mn), mercury (Hg), molybdenum (Mo), selenium (Se), silver (Ag), and zinc (Zn).

The presence of trace elements in ecosystems, the circulation of these elements in life processes, and their influence on metabolism is of interest to many fields of science including medicine, veterinary medicine, animal husbandry, as well as the science of human nutrition. Others looking at TEs come from science backgrounds relating to the physiology of plants, cultivation and fertilization, as well as the breeding of livestock, in which the possibility of controlling the presence of micronutrients may increase crop yields, produce better yields, and provide greater resistance to stresses caused by abiotic and biotic factors. There may also be opportunities to use TEs in the form of special fertilizers and agrochemicals to generate beneficial effects (e.g., for disease and drought resistance, as aids to flowering and maturing) and to fortify feed or food for health benefits. The presence of TEs in the environment shaped and shapes the three processes [4] whose final result is the dispersion and introduction of TEs into environmental circulation. Some of these elements significantly affected life processes, others did not play a significant role. The first process of the diffusion of trace elements occurred in the earth's crust during the creation of geological structures by geological processes. Unlike run dispersion processes for creating geological igneous rocks, the process of sedimentary and metamorphic rock formation is different. Elements in igneous rocks are scattered due to the crystallization of minerals from the liquid phase or solidification of magma deep in the earth's crust or solidification of magma on the surface. In this way igneous rocks are created. In the process of sedimentation or precipitation of the transferred aqueous suspension, elements in sedimentary rocks are dispersed. A different mechanism of dispersing elements happened when metamorphic rocks were created because the means of dispersal in the transformation of igneous, sedimentary, and metamorphic rocks occurred as a result of phase change and chemical processes under high pressure and temperature. Metamorphic processes not only changed the composition and scattering of elements but also changed the composition, structure, and texture of minerals in the rock. These processes create igneous rocks that occurred more than 4 billion years ago, and the processes of sedimentary rock from 700 million to 100 million years.

Elements and their compounds in the earth's crust have been dispersed as described earlier. Scattering of mercury, an element which is present partially in the liquid phase, happened differently to other elements. The process of mercury dispersion as a result of volcanic eruptions can be classified as part of the primary phase of scattering metals in the global environment. This phenomenon refers to a period more than 250 million years ago, when the mercury was liberated during intense volcanic activity in Siberia, which is considered as one of the main reasons why one of the mass extinctions in Earth's history occurred. Modern research suggests that accumulation of mercury observed in the Arctic may have accumulated by atmospheric forces and the polar rivers flowing into the Arctic sea [5]. Geologists from the University of Calgary have shown that the amount of mercury released at this time was 30‐times greater than the amount released in the volcanic activity we see today. The effect of this large‐scale release was catastrophic at a time when the continents were all joined together [5]. According to Dr. Benoit Beauchamp, professor of geology at the University of Calgary, Canada, these studies are significant because, for the first time, they link mercury to the Permian extinction. Of course, nature copes with such disasters, so after time, this mercury has been eliminated, falling in the form of mercury compounds to the bottom of the oceans. However, nature copes with pollution at a restricted rate, so the introduction of locally high amounts of mercury or other toxins can result in contamination over hundreds or even thousands of years [5].

The secondary dispersion of elements process saw the weathering of rocks forming the Earth's crust. The process of soil formation from various rocks containing TEs including arsenic (As), barium (Ba), beryllium (Be), cadmium (Cd), chromium (Cr), copper (Cu), fluoride (Fl), iodine (I), iron (Fe), lead (Pb), mercury (Hg), molybdenum (Mo), uranium (U), selenium (Se), vanadium (V), and zinc (Zn), caused elements naturally occurring in trace concentrations to be scattered. The movement of micronutrients to ecosystems in this way is connected to their availability for plants, animals, and humans. In addition, the natural processes of weathering of rocks support distribution trace elements. The tertiary dispersal process is associated with anthropological activities. Dispersal of elements in the third phase may be stored as waste, droppings, industrial wastewater, and municipal deposition gas and dust.

Knowledge of the content of trace elements in minerals, as well as their content in biological materials was, over a long period, limited to knowledge of the role of macro‐environment circulation and the role of elements in life processes. Over time this knowledge developed together with the development of analytical methods. The process of identifying elements at the concentrations of trace minerals in water, biomass, animal tissues, and medical analysis was different. The low sensitivity of analytical methods, high limits of detection, and low accuracy and reproducibility of the results contributed significantly to systematic errors in analyses of different matrices. Another factor negatively affecting the results of the analyses was an incorrect decomposition–digestion process used with the samples which was often conducted thermally on hot plate, a method which was associated with the issue of analyte loss. Such errors accounted for determining metals such as cadmium (Cd) and mercury (Hg).

2.3 The Role of Analytical Methods in the Research on Trace Elements

New ways of determining trace and ultra‐trace elements have naturally increased research capabilities and knowledge of the mechanisms of the role of elements in processes involving enzymes, hormones, and vitamins, and their interaction with the macro‐nutrient trace elements have required intensive research on organic nutrients, enzymes, vitamins, and hormones.

Revolutionary new analytical techniques naturally increased knowledge of TES in many disciplines but, at the same time, many theories were questioned as well as the data obtained on the role of TEs in life processes. This factor is not the fault of the researchers, but is a result of advances in analytical methods revealing that the problem of TEs is still current and requires further corrections and additions. Despite the huge number of publications, many complex and extremely valuable editions of books [6–14], there is a need for constant review of research in various fields and disciplines. The need for intensive research in understanding the impact of TEs is also necessary for changing the mechanisms and magnitude of impacts of anthropogenic activities on processes such as contamination of ecosystems, bioaccumulation, mobility of TEs, paths of dispersion and transportation, and speciation. Examples of such changes have seen the global withdrawal of lead compounds from motor fuels, the elimination of acid rains, radically marked decreases in emissions from conventional power plants, the widespread use of wastewater and water treatment, and the use of agrochemicals safe for health and the environment. Identifying the content of elements that are trace in water, soil, plants, animal tissues, body fluids, and organs of the human, as well as understanding the mechanisms and role of micronutrients in life processes, has created new possibilities for controlling the processes of life, such as stimulating plant growth by enriched fertilizer micronutrients, enrichment of livestock feed as well as food fortification with micronutrients for humans. In addition, knowledge of the role of TEs is used in the pharmaceutical industry and in the creation of food supplements.

In the history of the development of knowledge about TEs we can identify two separate trends: current cognitive and current practical applications. So, this is the story of the development of analytical methods and the history of the use of these elements in economic practices and processes on the border between biology and chemistry. The long history of the development of analytical methods has been shaped by successive discoveries in physics and chemistry and continuous improvement of analytical instruments. The second stream, current practical applications, is much more complicated and depends on the condition of raw material resources, technological, environmental, and lately even political situations and regulations.

Analytical quantitative methods based on the use of known chemical reactions with the application of volumetric methods, electrochemical methods, gravimetric and calorimetric methods, using stoichiometric principles, without separation and concentration of analytes for determination of trace metals did not allow for accurate determination of TEs. Only spectroscopy and spectrometric methods adopted for the determination of the chemical composition of the opportunity enabled accurate determination of TEs. Key facts from the development of spectrometric methods are as follows:

Spectroscopy has a very long history beginning nearly five centuries ago with the interests in solar radiation by Isaac Newton who introduced the term spectroscopy science. The beginning of this history saw investigations conducted by Athanasius Kircher (1646), Robert Boyle (1664), and Francesco Maria Grimaldi (1665), that built on Newton's earliest experiments in optics [15].

Research on emissions from a flame produced by burning an alcohol solution of salts conducted by Thomas Melville in Glasgow, 1752, formed the basis of flame spectrometry [16].

In 1776, Alessandro Volta proposed the use of sparks for chemical determination on the basis of experiments with static electric charges strong enough to create sparks [17].

In 1814, Joseph von Fraunhofer analyzed the emission spectrum emitted by flames, sparks, and the spectrum of the sun and stars and mapped nearly six hundred absorption lines thereby creating the basis for the construction of spectrometers [18].

In 1859, Gustaf Kirchhoff together with Robert Bunsen selected sharp line emission spectra lines and recognized these lines as characteristic spectral lines of specific elements. Thanks to a special type of burner constructed by Robert Bunsen and earlier experiments they could apply the spectrometric method for the quantitative determination of cesium (Cs), rubidium (Rb), thallium (Tl), and indium (In) [19].

In the late 1920s Swedish agronomist Lundegårdh introduced the analysis of micronutrients by the flame spectrometry method using pneumatic nebulization with argon analyzed solutions to agricultural practice. These spectrometers were also used in the analysis of potassium (K), sodium (Na), calcium (Ca), and magnesium (Mg) as TEs in blood and urine used in medical investigations [20].

Since the beginning of the twentieth century there have been multidirectional explorations of the different solutions of radiation sources and analysis of the emitted spectrum. The result of the research and development work was the development of spectrometers with electric arcs and sparks for quantitative TE determination. Developments in the instrumentation area led to the application of atomic spectroscopy in the field of analytical chemistry applied in medicine, agriculture, geology, biophysics, and ecotoxicology. In the next generation of spectrometry various types of absorption, emission, and luminescence spectrometric methods were seen [18]. This includes atomic absorption spectrometry (AAS), an analytical technique that allows for the determination of elements in liquid, solid, and gaseous samples. The measuring principle is based on the phenomenon of the absorption of radiation at a specific wavelength by free metal atoms. AAS can be used to determine over 70 different elements in solution or directly in solid samples. Limitations of the flame spectroscopy method were too low a flame temperature which limited excitation of atoms of elements and the absorption method using a fixed radiation source (a lamp in AAS) limits analysis to the determination of only a single element. In the 1960s a number of varieties of spectroscopic methods, including the ones tailored for the analysis of solids such as graphite furnace atomic absorption spectroscopy (GFAAS), stabilized temperature platform (STPF) methods, as well as solutions using Zeeman background correction for interference reduction were developed [21].

In 1941, in order to practice the analytical determination of TEs, spectrophotometers, devices based on a concept developed by Arnold Beckmann, were introduced. This measuring technique is a quantitative measurement of transmission or reflection of light through a sample. This technique was an important tool for reflection and absorption spectroscopy in the near ultraviolet and visible light, and formerly also in the infrared, finding wide applications in analytical chemistry, biology, agriculture, medicine, and materials research.

In 1961, T.B. Reed presented the method of inductively coupled plasma (ICP) operating at atmospheric pressure [21] while the design of the analytical potency and analytical capabilities for determination of TEs in 1964 were presented by Stanley Greenfield [22]. The practical dissemination of this technique has been enhanced by companies building analytical equipment. Examples include, Agilent, Perkin‐Elmer, Philips, Varian, Skyray, Analytic Jena, Thermo, NU Instruments, Horiba, GBC Scientific. The first instruments were ICP‐OES spectrometers equipped with optical detectors of spectral lines, and then ICP‐MS spectrometers equipped with detection system storage, capable of detecting TEs and even analyzing the different isotopes. Expansion of the ICP‐MS technique with laser ablation allows direct analyses even of solid materials. The LA‐ICP‐MS technique is useful for in situ analyses of TEs in solid biological and environmental samples. Different methods employing ICP include new hybrid methods such as liquid chromatography–inductively coupled plasma mass spectrometry (LC‐ICP‐MS) and gas chromatography–inductively coupled plasma mass spectrometry (GC‐ICP‐MS).

Spectrometric methods based on ICP using various sources of detection have created extremely useful learning tools for identifying not only TEs but also ultratrace elements, where it is possible to determine in practice all types of samples with extremely low levels of detection with high accuracy and repeatability. These methods also have an advantage over atomic absorption spectrometry (AAS) as they allow the simultaneous analysis of large numbers of TEs and enable the determination of elements at concentrations: ppm, ppb, and even ppt. An important factor is that spectroscopic methods make it possible to eliminate interferences. At present, analytical techniques offer a range of hybrid solutions tailored for specific samples, such as liquid chromatography‐inductively coupled plasma mass spectrometry (LC‐ICP‐MS, gas chromatography‐inductively coupled plasma mass spectrometry (GC‐ICP‐MS, and laser ablation inductively coupled mass spectrometry (LA‐ICP‐MS).

Section 2.3 discusses the role of analytical methods in TE research and the basics of analytical techniques and their advantages and limitations are presented. The evolution of analytical tools that increase the potential of research on the role of TEs in the processes of life and the environment are also mentioned. By bringing together different analytical techniques it is possible to implement hybrid techniques, combining the analytical methods formed in series or in parallel as connected modules of various analytical techniques. Such solutions are liquid chromatography–infrared spectroscopy gas chromatography–mass spectrometry, capillary electrophoresis–mass spectrometry, liquid chromatography–mass spectrometry gas chromatography–infrared spectroscopy, and liquid chromatography–NMR spectroscopy.

In addition to the dominance in recent years by the ICP and AAS methods in the various embodiments of apparatus, great progress has been made on reducing the level of detection in methods such as spectrofluorimetry, fluorimetry, fluorescence spectroscopy, and thus in methods of spectrographic electromagnetic radiation in analyzing fluorescence generating ultraviolet light or X‐ray. Although these methods are dedicated to organic chemistry and biochemistry they also allow the determination of compounds containing trace metals bound in the form of complexes with organic ligands. Accuracy and reliability of trace element analysis are affected not only by the precision and sensitivity of the detectors, the final analysis, but also by an important step in the analytical procedures which is mineralization of environmental samples to obtain analytes suitable for performing analysis on using modern equipment. The process of mineralization results in analytical losses of analyzed TEs due to wet digestion in open vessels on a hot plate. Since the introduction of microwave digesters in the form of the sealed Teflon vessels from the beginning of the 1970s, the inconveniences of this method were eliminated. A second way used to eliminate this nuisance was the use of hybrid methods, such as laser ablation with a combination of ICP and AAS with direct simultaneous decomposition and determination (e.g., analysis of mercury directly from solid samples). An interesting recent analytical tool used to analyze the distribution of trace metals on the surface of samples is the application of optical microscopy, electron microscopy, and scanning electron microscopy.

2.4 The History of Research on Trace Elements

The development of knowledge about the role of TEs is strictly dependent on progress in the field of analytical methods, complex analytical procedures, and construction of new analytical equipment. An important role is played by analysts who publish their work in the Journal of Trace Element Analysis which is a peer‐reviewed international journal devoted to all aspects of TE analysis and which provides a platform for researchers to discuss new issues and promote developments in TE determination. Research results and analytical problems are also published in the following journals: Biological Trace Element Research, Journal of Trace Elements in Medicine and Biology, Journal of Trace Elements in Experimental Medicine, Trends in Environmental Analytical Chemistry, Analytical Biochemistry: Methods in the Biological Sciences.

The interest in social, economic, and also medical aspects of TEs is associated with the tertiary dispersal process[4]. In an environment dominated by anthropogenic sources two periods that were fundamentally different can be identified. The first period assessed the impact of some elements affecting life processes on the basis of determining cause and effect or searching for the correlation between the source of these elements and the effects on, for example, the health of the people exposed to these elements. The second period was shaped by progress in the field of analyzing TEs and virtually every year tools for the identification of elements at very low concentrations were made available to scientists from different disciplines. The beginning of this second period is the second half of the nineteenth century.

In ancient times several metals in life processes were discovered as trace elements as a result of concentration in metallurgical processes that were obtained. The history of human relationships with these elements, which are now referred to as TEs, were in ancient times focused on gold (Au) and silver (Ag), precious metals for aesthetic (jewelry) purposes and for their values ​​for treasury (making coins and insignia). Other elements such as iron (Fe), copper (Cu), zinc (Zn), and tin (Sn), were used in the manufacture of dishes, cups, weapons, tools, and for construction and monument building. Elements that had toxic effects such as mercury (Hg), arsenic (As), and lead (Pb) were also used, but in practice damaged life, affected health, and polluted the environment. This latter group of elements used in compounds caused many drastic events in the history of mankind. Very often people do not realize that these elements lay behind the real causes of various social woes. This applies to the inappropriate use of mercury compounds, lead, and arsenic which are harmful to health and the environment. A spectacular example of unanticipated adverse effects in ancient Rome, the Eternal City, saw a deterioration in the health of its inhabitants as a result of contaminated drinking water by lead compounds derived from lead pipes supplying water from the aqueducts. These health effects were one of the reasons for the collapse of this ancient metropolis. Modern study of ancient sediments in the vicinity of Rome conducted by geochemist Jerome Nriagu [23] clearly indicated that the cause of the mass lead poisoning of the residents of Rome was the presence of lead not only in water, but also from the dishes, plates, and cups. Nriagu's theory has been confirmed by studies conducted by an international team [24] looking at sediments from the channel connecting the Tiber to the sea near Rome and the fact that morbidity caused by lead increased after the year 554 AD in the repaired aqueducts. The repair of aqueducts may have resulted in leaching water that had been standing for a long time in the unused pipe, which contained a lot of detrimental elements. Despite often held beliefs, the Romans were aware of the risks associated with lead pipes. The Roman architect Vitruvius, in his work on the building of ancient Rome, Ten Books about Architecture, recommended the use of vitrified clay pipes because lead can be harmful to the human body. Vitruvius wrote about the dangers of such practices, Water flowing through clay pipes is healthier than the one passed by the lead. You can say even more – that the water of lead is harmful. The truth of this statement can be confirmed by observing the people working with that metal, who are very pale. [25]. In ancient Rome, there were not only TEs in drinking water, but also in wine, of which the Romans drunk large volumes. The local wine was in fact stored and sweetened using substances such as sapa or defrutum [26]. Dense sweet juices from grapes were cooked in lead kettles. The daily dose of lead caused by drinking a liter of wine a day causes equivalent damage to the daily dose of lead the Romans were exposed to, leading to infertility disorders, neurological diseases, and sometimes even death. Lead compounds were also an important component of the Roman cosmetics. Red oxide of lead, described as red lead, was used to redden the cheeks. White lead carbonate (cerussite) was the basis for powders. A recipe is given for make‐up in a poem by Ovid, guaranteeing that these cosmetics will make the face of every woman beautiful and attractive, and some Roman doctors recommended the suspension of some of the oil of lead compounds to be used as a contraceptive. There is no doubt that such treatments had serious consequences for health. Obtained by man lead compounds penetrate into the bloodstream, where the lead is incorporated into red blood cells, soft tissue, and bone. Bones accumulated lead in the form of compounds and colloidal crystal. Evidence of the effect of bioaccumulation of lead in skeletons was found in Pompeii, where bones were found to contain nearly thirty times more lead than those of people living in the ancient countryside [24, 25]. One of the causes of environmental mercury poisoning was the use of mercury in obtaining gold. Gold‐bearing rock was crushed and then treated with mercury to distill the resulting liquid mercury amalgam. This method has been used in the Andes and the Amazon without any safety precautions and caused mercury poisoning. The Romans also used mercury to leach river sands in order to extract silver and gold from them. In the Middle Ages, alchemists tried to create gold by combining sulfur with mercury [24, 25].

Another form of dispersion of mercury was the use of mercury compounds in cosmetics and as a special medicine. Mercury oxide (II) was the major component of the red color used as lipstick and as paint. In the sixteenth century, Paracelsus introduced mercury compounds as a pharmaceutical agent. In ancient times mixtures containing orpiment and realgar were used to treat diseases of the lungs and skin. In the eighteenth and nineteenth centuries arsenic agents were used in the form of pastes, solutions, tablets, and intravenous and subcutaneous injections, used to combat most diseases: malaria, rheumatism, asthma, tuberculosis, diabetes, hypertension, stomach ulcers, psoriasis, heartburn, eczema, and leukemia. Almost all the drugs containing arsenic agents were withdrawn from the market mainly due to carcinogenicity, despite their high efficiency.

In ancient times, mercury compounds, lead, and arsenic were used to produce poisons, for political purposes, as well in the execution of prisoners. The works of Pliny the Elder, Dioscorides, Scribonius, Largus, and Galen, detail the information on poisons containing these elements which were distinct from those of vegetable or animal origin. As cases of poisoning increased as a kind of epidemic they were required to stop by law. In 82 BC, in an attempt to stop poisonings, the Roman dictator Lucius Cornelius Sulla, the constitutional reformer, gave Lex Cornelia, the first law to protect against poisoning.

The tertiary dispersal of TEs in the environment from anthropogenic sources had local influence and character, and concerned specific agglomerations. A specific form of the distribution of TEs can be seen through the spread of various formulations made from these elements which were used as cosmetics, pigments, paints, and pharmaceuticals. The detrimental source of emissions, although limited in extent, were related to melt metals and waste deposits. Actual anthropogenic impacts of industry took place in the first half of the nineteenth century, and developed simultaneously with the first and second industrial revolution. Rapid development of industry based on intensive use of mineral resources, without treatment, without purification of gases and fumes, and without utilization of wastes, resulted in a significant enrichment of basic environmental media such as soil, vegetation, water, and air, the formation of which was the so‐called geochemical neoanomalies, in which the content of trace metals was up to 1000‐times greater in comparison with the content of these elements in the earth's crust. Environmental pollution has been created by situations of the low efficiencies of technological processes, high specific energy consumption, as well as the location of industrial plants, usually within urban areas. This situation resulted in an increase of toxic compounds in plants, food, water, and air. Creating neoanomalies has strongly deformed natural geochemical cycles. The phenomenon of neoanomalies occurred simultaneously with the development of manufacturing industries and mining. The turning point stopping increasing environmental pollution was in international political intervention. Secretary‐General of the United Nations, U Thant, in the General Assembly on May 26, 1969, presented the report, Problems of the Human Environment, (Resolution 2398) which documented for the first time in the history of world an official opinion on the profound changes being seen in the environment as a result of pollution from scientific and technological developments. The data presented indicated global environmental degradation, gave reasons for this situation, and brought attention to adverse consequences for the further development of civilization. The report called on the leaders of the world to use rationally the Earth's resources and promoted efforts to protect the global ecosystem. The report documented facts that for the first time in the history of mankind there was an ecological crisis